1. Field of the Invention
The present invention relates to the manufacture of cold-cure, closed-mold, flexible, high resilience, foamed polymeric materials by reacting a polyol with an organic polyisocyanate.
2. Description of the Prior Art
Since about 1969, improved load-bearing polyurethane foams have appeared which are variously described as "cold-cure, closed-molded" or "high resiliency" foams. New techniques were developed to make small, molded flexible foam parts without the need for high temperature cure ovens used for producing conventional toluene diisocyanate-based so called "hot cure" foams. Typically, these "cold-cure" foams were produced using a combination of an ethylene oxide capped triol having a molecular weight of between 3000 and 5000 with crude polymethylene polyphenylisocyanate. Using these new techniques, foam is produced using molds heated to a temperature of 80.degree. to 120.degree. F. The foam can be stripped from the mold within 3 to 10 minutes subsequent to pouring, resulting in a considerable saving in processing time over the 15- to 20-minute mold time required using the prior hot molding conditions wherein the mold is heated to a temperature of 300.degree. to 350.degree. F. The high resilience, flexible foams produced by the cold-cure methods possess improved flex fatigue characteristics and inherently better flame retardance as well as improved load-bearing characteristics; the sag factor approaching that of a conventional rubber latex foam.
It is known to use an inorganic base compound such as sodium hydroxide or the salt of a strong inorganic base and a weak inorganic acid as illustrated by sodium carbonate as a catalyst for the reaction of a polyol with a diisocyanate to produce a flexible, resilient foam. Polyether polyols and polyesters are disclosed in U.S. Pat. No. 3,108,975 as useful in combination with a polyisocyanate and water in the formation, by a hot-cure process, of a flexible, resilient foam. Either a strong inorganic base or certain inorganic salts of a strong base and a weak acid are disclosed as catalysts for the reaction.
The use of sodium carbonate as a catalyst in the preparation of flexible polyurethane "cold cure" foams by the reaction of a polymeric polyol with tolylene diisocyanate is disclosed in U.S. Pat. No. 3,943,075. The foams produced are obtained by a "free-rise" process. Both tertiary organic bases and inorganic basic catalysts are disclosed as useful in producing a polyurethane foam from a diisocyanate and a polyol in U.S. Pat. No. 3,336,242. Besides metallic oxides and hydroxides, tertiary organic bases such as trimethylamine and ethyl-N-methyl morpholine are disclosed as useful for producing a polyurethane foam by the so called "one-shot" method. In Japanese Pat. No. 51,109,100, there is disclosed the use of an amine and/or an organic tin compound as a catalyst (for the production of polyurethane foam from the reaction of polyols and isocyanates) in combination with (1) a water-containing alkali metal compound, i.e., the sodium salt of carbonic acid, and (2) a special granular inorganic material which foams on heating. In U.S. Pat. No. 3,112,281 there is disclosed the preparation of a polyurethane foam by the reaction of a polyisocyanate with a polyhydric polyether having within the molecule a tertiary amine. It is noted that the polyether is supplied at a pH of about 8 to about 11 and can contain residual amounts of sodium hydroxide.
In no one of these references is there disclosed or suggested the reaction of an organic polyisocyanate and a polyol to produce a high resilience foam in the presence of a co-catalyst combination of a metal-containing basic catalyst with a tertiary amine catalyst to provide a foam having improved properties.
The preferred polyol, which is a graft copolymer dispersion of a vinyl monomer in a polyol having unsaturation is disclosed in U.S. Pat. No. 3,823,201. However, there is no indication therein that polyurethane foams having superior physical properties, as described herein, can be prepared therewith using the co-catalysts disclosed herein.